Ferrule and method of manufacturing the ferrule

ABSTRACT

To provide a ferrule of any desired length while maintaining axial alignment of optical fibers. A plurality of ferrule components  30  having one or two or more fine holes 31 in which an optical fiber  4  is inserted are connected along an insertion direction of the optical fiber  4.

TECHNICAL FIELD

The present invention relates to a ferrule of an optical communicationconnector.

BACKGROUND ART

Optical fiber communications have already been introduced for relaysystems connecting between telephone exchange stations on account ofenabling ultrahigh transmission at low costs. Thus, the futureintroduction of the optical fiber communications in each subscriber'ssystem is being under study. Optical fibers as a transmission medium areconnected together in such optical communications to build a network,and terminal ends thereof are connected to modules or terminal devices.An optical communication connector functions to detachably connect theoptical fibers etc. The optical communication connector includes: plugseach incorporating a ferrule and inserted face to face; and an adapterhaving a built-in sleeve allowing the insertion of the plugs from bothends thereof. When the plugs are inserted from both ends of the adapter,the ends of the two ferrules butt against each other inside the sleeve.The optical fibers inserted in the ferrules are aligned and opticallyconnected to each other. Upon this connection, the ferrule incorporatedin the connector protects frangible optical fibers and aids in the axialalignment of the optical fibers to prevent an optical loss due to anoff-axis arrangement of the optical fibers or gap therebetween.

As mentioned above, in order to enhance the axial alignment accuracy forthe optical fibers to thereby prevent an optical loss, it is necessaryto align the axes of insertion holes for an optical fiber formed in theferrule, which requires highly precise polishing of centering theinsertion hole with the center of the outer diameter of the ferrule. Toexplain a specific manufacturing method therefor, first, a mixture ofzirconia power and resin is used as a raw material, and the material ismolded through injection molding or extrusion molding into a cylindricalmember, followed by baking at about 500° C. to degrade a resin componentand then baking at as high temperature as about 1,200° C. to therebyyield a baked member. Subsequently, copper wire such as music wireapplied with a diamond abrasive is passed through the cylindrical bakedmember along its central axis. Then, the inner surface of the insertionhole is polished and in addition, the size of the insertion hole isadjusted. Finally, the outer surface of the ferrule is polished, and theferrule thus surface-finished is perforated at the center to formoptical fiber insertion holes.

However, it is not easy to perforate the ferrule along its central axisto form the optical fiber insertion holes without involving any off-axismisalignment. This polishing is disadvantageously complicated and costshigh. In addition, considering the difficulty of such machining,specifications (length and the number of cores) of the ferrule should bemade uniform. Hence, there arises a problem in that a variety offerrules cannot be provided in large volumes.

DISCLOSURE OF THE INVENTION

The present invention has been made in view of the above-mentionedproblems of conventional techniques, and it is therefore an object ofthe present invention to provide a ferrule capable of maintaining axialalignment of optical fibers with higher accuracy.

In order to achieve the aforementioned object, according to the presentinvention, an optical communication ferrule for receiving an insertedoptical fiber includes a plurality of ferrule components having one ortwo or more fine holes in which the optical fiber is inserted andconnected together along an insertion direction of the optical fiber.

The perforation precision can be further enhanced by forming fine holesin the individual ferrule components to be connected rather than formingthe fine hole in the entire ferrule since the perforation depth for eachperforation can be made smaller. Hence, the fine holes can be formed soas to exactly pass the center of the outer diameter of the ferrule in astraight line. As a result, the optical fibers to be inserted into thefine holes are aligned with no off-axis portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a connector including a ferruleaccording to an embodiment of the present invention.

FIG. 2(a) shows an example of the ferrule according to the embodiment ofthe present invention as viewed from an insertion direction of anoptical fiber.

FIG. 2(b) is a side view of the ferrule of FIG. 2(a).

FIG. 3(a) shows another example of the ferrule according to theembodiment of the present invention as viewed from the insertiondirection of the optical fiber.

FIG. 3(b) is a side view of the ferrule of FIG. 3(a).

FIG. 4(a) is a side view of an example of a machining device for aferrule component according to the embodiment of the present invention.

FIG. 4 (b) is a front view of the machining device of FIG. 4(a)

EMBODIMENT MODE OF THE INVENTION

A ferrule according to the present invention is an optical communicationferrule for receiving an inserted optical fiber, including a pluralityof ferrule components having one or two or more fine holes in which theoptical fiber is inserted, the ferrule components being connected toeach other along an insertion direction of the optical fiber toconstitute the ferrule.

In the present invention, the plurality of ferrule components arepreferably connected such that the one or two or more fine holes of theferrule components to be connected are arranged in substantially astraight line.

Further, the one or two or more fine holes in the ferrule components arepreferably expanded in a tapered form on at least one ends thereof.

Besides, the ferrule component preferably includes: an adhesive fillingrecess or protrusion; and an injection groove for injecting an adhesivefrom the outside to the adhesive filling recess or protrusion, forexample, an injection groove communicating with the outside and therecess or protrusion and connecting therebetween.

In addition, the ferrule component preferably includes an engagementportion engaged with a connector housing where the ferrule is set.

Further, the ferrule component preferably contains zirconia ceramicsalthough not particularly limited, and can be formed of stainless steel,hard steel, alloy, a resin material, or other metal or non-metalmaterials aside from zirconia ceramics. Needless to say, this does notnecessarily imply that the same material should be used for all theferrule components to be connected, and ferrule components made ofdifferent materials can be combined and connected.

According to the present invention, the ferrule components having one ortwo or more fine holes in which the optical fibers are inserted areconnected along the insertion direction of the optical fiber toconstitute the ferrule. The number of ferrule components constitutingthe ferrule is not limited, so an arbitrary number of ferrule componentsare connected into a desired length. Also, the length and shape of theone or two or more ferrule components are not limited. The ferrulecomponents may be uniform or different in length, and the ferrules mayhave a cylindrical shape, a rectangular-column shape, or other suchshape. Further, the number of fine holes for the optical fiber in theferrule components may be one or two or more. The resulting ferrule maybe a single-core, double-core, 4-core, 8-core, 16-core, 32-core, ormulti-core ferrule. The arrangement and inter-core pitch of the fineholes can be freely set. In this case, the ferrule components arepreferably connected such that the fine holes are arranged insubstantially a straight line. Thus, it is possible to obtain a desiredferrule by appropriately combining the ferrule components of variousshapes, sizes, and specifications in conformity to specifications suchas shapes and sizes of the ferrule.

Also, the perforation precision can be further enhanced by forming thefine holes in the individual ferrule components to be connected ratherthan forming the fine hole in the entire ferrule since the perforationdepth for each perforation can be made smaller. Hence, the fine holescan be formed so as to exactly pass the center of the outer diameter ofthe ferrule in the straight line. As a result, the optical fibers to beinserted into the fine holes are aligned with no off-axis portion.

In this way, according to the present invention, it is possible toprovide a ferrule capable of maintaining the axial alignment of theoptical fibers and conformable to various specifications.

A manufacturing method for a ferrule according to the present inventionis a manufacturing method for an optical communication ferrule thatreceives an inserted optical fiber, including perforating in a pluralityof ferrule components one or two or more fine holes in which the opticalfiber is inserted, and connecting the ferrule components having the fineholes perforated therein such that the fine holes are arranged insubstantially a straight line.

According to the present invention, the ferrule component preferably hasa width of about 3 mm or smaller, more preferably about 2 mm or smalleralong an arranging direction of the perforated fine holes.

According to the present invention, a predetermined number of fine holesof a desired hole diameter are formed in predetermined positions of theferrule components, and the ferrule components are connected such thatthe fine holes thereof are arranged in substantially a straight line.

Consequently, a ferrule equivalent to the ferrule according to thepresent invention can be obtained. Further, the manufacturing method ofthe present invention can reduce the perforation depth in the step ofperforating the fine holes for optical fibber, whereby it is possible toappropriately change the number of fine holes, and their arrangement orsize while keeping the perforation precision high. Hence, ahigh-performance ferrule capable of maintaining the axial alignment ofthe optical fibers with high precision and conformable to variousspecifications can be manufactured at low costs.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the present invention will be describedwith reference to the drawings. FIG. 1 is a perspective view of aconnector including a ferrule according to this embodiment. FIGS. 2 showthe ferrule according to this embodiment. FIGS. 3 show another exampleof the ferrule according to this embodiment. FIGS. 4 show a machiningdevice for a ferrule component.

Referring to FIGS. 1 to 3, a ferrule 3 according to this embodiment isfirst described. FIG. 1 shows a connector 1 having the ferrule 3incorporated therein, and illustrates arrangement of the ferrules 3 forconnection in the optical communications.

A network built of optical fibers 4 is connected with individualcomputers, communication apparatuses, and other terminal devices. Theconnector 1 including detachably attachable adapter 1 a and plug 1 bfunctions to establish such connections.

The connector 1 of FIG. 1 includes two plugs 1 b having the ferrules 3incorporated therein, and the adapter 1 a having a built-in sleeve 5allowing insertion of the plugs 1 b from both ends. When the plugs 1 bare inserted from both ends of the adapter 1 a, the ends of the twoferrules 3 butt against each other inside the sleeve 5 by the action ofan elastic member (not shown) built in the adapter 1 a, whereby theoptical fibers 4 in the ferrules 3 are arranged in a straight line, andinformation is transmitted through the connector 1. An optical lossresults from the off-axis arrangement of the butting ferrules 3 or gapsthere between. To avoid such losses, the ferrules 3 are required to havethe functions of supporting the ends of the optical fibers 4 such thatthe two optical fibers 4 are connected straight as well as protectingthe optical fibers 4 as an information transmission medium.

Referring next to FIGS. 2 and 3, the ferrule 3 having a characteristicstructure is described. The ferrule 3 according to this embodiment isillustrated in FIGS. 2 and 3; the ferrule 3 has a cylindrical shape inFIG. 2 and a rectangular-column shape in FIG. 3. These are the same inbasic structure and hence, this embodiment is described centering on theferrule of FIG. 2.

FIG. 2(a) shows the ferrule 3 as viewed from the insertion direction ofthe optical fiber 4, and FIG. 2(b) is a side view of the ferrule 3.

As shown in FIG. 2(a), the ferrule 3 is a double-core one. Two fineholes 31 are formed along the insertion direction of the optical fiber4. A tapered peripheral portion 32 surrounds each fine hole 31 and formsa surface sloping toward the fine hole 31. Also, provided around theperiphery of the ferrule 3 are adhesive filling portions 33 filled withan adhesive for reinforcing the connection between ferrule components30, and an engagement portion 35 adapted to engage with a connectorhousing 2 that is omitted from FIGS. 2. The engagement portion 35 isstructured in conformity to the structure of the connector housing 2 andthus its shape is not particularly limited.

When viewed from the side, the ferrule 3 according to this embodiment isstructured by connecting three ferrule components 30 a, 30 b, and 30 cas shown in FIG. 2(b). There is no particular limitation on materialsfor each ferrule component 30, and the ferrule components can be formedof stainless steel, hard steel, alloy, a resin material, or other metalor non-metal materials. Note that, the ferrule 3 butts against the otherferrule 3 when in use, so if the two ferrules 3 are different inhardness, lower-hardness one of the two may be cracked (broken). Hence,it is preferable to select a material according to the hardness of theother ferrule 3 to be connected. For example, when the other ferrule 3to be connected contains zirconia ceramics, a material having anequivalent same zirconia ceramics content is preferably selected. Here,the ferrule components 30 (30 a, 30 b, and 30 c) to be connected may beformed of different materials. In this embodiment, out of the ferrulecomponents, only the ferrule component 30 a to butt against the otherferrule is formed of zirconia ceramics, while the remaining ferrulecomponents 30 b and 30 c are formed of a resin material. With thisstructure, the hardness of the butting portion between the ferrules 30can be held high and in addition, the total cost of the ferrule 3 can belowered.

A process material for each ferrule component 30 first undergoesprecision polishing into a smooth surface with an unevenness toleranceof 0.002 mm or smaller. At this time, the surface roughness Ra ispreferably 0.05 or more. If the ferrule 3 has a cylindrical shape, thatis, if each ferrule component 30 has a circular shape, its diameter isset to about 1.0 mm to 3.0 mm. The entire length thereof ranges about200 mm to 1,000 mm. Then, the process material is sliced into eachferrule component 30. The width of each ferrule component 30 along theinsertion direction of the optical fiber 4 is preferably 3 mm orsmaller, more preferably 2 mm or smaller for facilitating theperforation process. This width is preferably determined as appropriateaccording to the diameter and hardness of the ferrule, and the diameterof the fine holes 31 to be formed. Accordingly, in this embodiment, thewidth of the ferrule component 30 a made of zirconia ceramics is set to2 mm or smaller from the viewpoint of perforation precision. Theresin-made ferrule components 30 b and 30 c are designed to have a widthof 2 mm or more. In slicing the process material, considering thesubsequent polishing process, it is preferable to slice the materialinto the ferrule components 30 with a margin of about 0.003 mm allowedfor their predetermined widths. In this way, the ferrule components 30different in length are used in combination, thus providing the ferrule4 of a desired length. At this time, lengths of the resin-made ferrulecomponents 30 b and 30 c are variously set, whereby the total cost ofthe ferrule 4 can be lowered while the ferrule 4 of any desired lengthcan be obtained.

The sliced ferrule components 30 undergo precision polishing again intoa prescribed size, followed by perforation with a machining device. Inthis embodiment, the ferrule component 30 a made of a materialcontaining zirconia ceramics is perforated to form the fine hole 31having a diameter of 0.125 mm+0.001 mm=0.126 mm or less. The resin-madeferrule components 30 b and 30 c are perforated to form the fine hole 31having a diameter of 0.125 mm+0.075 mm=0.200 mm. Besides, the number ofthe optical fibers 4 may be one or two or more. Thus, the fine holes 31may be formed in a corresponding number to produce a single-core,double-core, 4-core, . . . , or 32-core ferrule, for example.

Further, the fine holes 31 have the tapered peripheral portion 32 on atleast one ends. There is a possibility that the ferrule components 30involving even a slight off-axis portion make it impossible to arrangethe fine holes 31 straight with accuracy because of their extremelysmall hole diameter. Further, the optical fiber 4 is frangible and thusmay be damaged by even a small impact. In this embodiment, the ends ofthe fine holes 31, which are aligned straight when the ferrules 3 areconnected to each other, are tapered so as to expand at each position ofthe junction between the ferrule components 30. With this structure,when the optical fiber 4 inserted into the fine hole 31 is to beinserted into the fine hole 31 of the adjacent ferrule component 30, theoptical fiber is inserted into the widely open end of the fine hole 31,whereby the tip end of the optical fiber 4 is guided to the center ofthe fine hole 31 along the slope forming a tapered shape whose diametergradually decreases toward the insertion direction. Hence, the opticalfiber 4 can be inserted into the next fine hole 31 of the adjacentferrule component 30 with no damage.

Next, description is given of means for connecting the ferrulecomponents 30 thus machined. The ferrule components 30 are preferablyconnected such that the fine holes 31 thereof are arranged insubstantially a straight line. In particular, the multi-core ferrulecomponents 30 are preferably first positioned so as not to causedisplacement of each fine hole 31, and then engaged and bonded together.To elaborate, the ferrule components 30 are arranged in such a directionas to align the fine holes 31 in substantially a straight line. A musicwire is passed through the fine holes 31 and the ferrule components areroughly secured in position and then temporarily caulked with a jig suchas caulking and optionally engaged with one another if any engagementportion is provided. Further, the adhesive is filled in the adhesivefilling portion 33 through an injection groove 34, and the music wire isremoved after the adhesive is solidified and the ferrule components 31are firmly connected to thereby bring the ferrule 3 to completion.

To give additional explanation about the connection between the ferrulecomponents 30, the ferrule components 30 to be connected preferably havean engagement member or bonding portion that allows engagement with theadjacent ferrule component. In order to form the bonding portion, theadhesive filling recesses or protrusions 33 are preferably formed ineach ferrule component 30, with the recesses or protrusions defining thespace for filling the adhesive when the ferrule components 30 arearranged side by side. In this embodiment, the adhesive filling portions33 for filling the adhesive used for bonding the adjacent ferrulecomponents 30 are provided. The adhesive filling portions 33 arerecesses formed at the interface between the ferrule components 30(interface with the other ferrule component); when the components areconnected together, the recesses face each other to thereby define aspace, and the adhesive is injected into the space and functions toreinforce the connection between the adjacent ferrule components 30. Forinjecting the adhesive from the outside, the injection grooves 34communicating with each adhesive filling portion 33 are formed in thisembodiment. This groove maybe formed in either one of the adjacentferrule components (30 a and 30 b), (30 b and 30 c). Alternatively, thegroove may be formed therebetween. The injection grooves 34 communicatewith the adhesive filling portions 33 from an injection port throughwhich the adhesive is injected, and further with the outlet. Theadhesive injected from the injection port fills the adhesive fillingportion 34 and then flows toward the outlet. It is judged from theadhesive exuding from the outlet that the adhesive filling portion 34has been filled up with the adhesive. Thereafter, the whole is fixed andthe adhesive is left to solidify. This enables the external injection ofthe adhesive and connection between the ferrule components 30 withoutadversely affecting the optical fiber inside the ferrule 4.

As mentioned above, according to this embodiment, by combining theferrule components 30 as appropriate, the ferrule 3 conforming todesired specifications can be obtained, and the material for the ferrulecomponents 30 can be selected on a per-component basis, resulting incost reduction of the ferrule 3. Further, the ferrule 3 is divided intothe ferrule components 30, and the machining is effected not on theentire ferrule 3 but on each ferrule component 30, whereby theperforation depth can be made short, and the number of fine holes to beformed, the inter-core pitch, the core diameter, etc. can be variouslychanged to thereby provide the ferrules 3 conforming to variousspecifications while maintaining the machining accuracy.

Note that as mentioned above, the ferrule 3 of FIGS. 3 is the same asthat of FIGS. 2 except that its shape is a rectangular-column shape, andhence repetitive description thereof is omitted here.

Next, referring to FIGS. 4, a machining device 7 for the ferrule 3according to this embodiment is described. FIG. 4(a) is a side view ofthe machining device 7, and FIG. 4(b) is a front view of the machiningdevice 7.

As shown in FIGS. 4(a) and 4(b), the machining device 7 has a vibrationabsorption base 15 as a base, and a column 8 standing substantiallyupright on the base and supporting a motor holding plate 10 that holds amotor 9. A cutting tool 13, which perforates the target material bymeans of torque transmitted from the motor 9, is used to form the fineholes 31 in the ferrule components 30. A work 14 is held by a work chuck16 placed on the upper surface of the vibration adsorption base 15. Theoriginal position (set position) of the work 14 is determined based oninformation on positions measured with an optical sensor 11, and a dogchunk 12 holds the work 14 in an appropriate position. After the work 14to be machined (ferrule component 30) is set, the cutting tool 13perforates the work with submicron-order precision. In this embodiment,an NC machine tool is adopted as the machining device 7. The use of theNC machine tool enables the position or number (core number) of the fineholes 31 to be appropriately set only by inputting numerical values.

The machining of the ferrule components 30 with the machining device 7is basically the same as the aforementioned machining of the ferrulecomponents 30. That is, a cylindrical or rectangular-column moldedproduct prepared through the extrusion molding or the like is polishedwith a surface polishing device (not shown) and sliced with a slicercomposed of a diamond blade, followed by polishing the sliced surfacesdown to the length corresponding to a desired width of the ferrulecomponents 30. The polished ferrule components 30 are placed on themachining device 7 and perforated so as to allow the fine holes 31 to beformed in the vertical direction. Although depending on thespecifications of the machining device 7, when perforated to form thefine holes 31 having a diameter of 0.125 mm, the ferrule components 30preferably have a thickness (in the perforation direction) of 3 mm orsmaller, particularly preferably 2 mm or smaller, with which theoff-axis misalignment of the fine holes 31 is minimized. After the fineholes 31 are formed, the edges of the fine holes 31 are ground andtapered to define the tapered peripheral portion 32 and in addition,form the adhesive filling portion 33 and the injection groove 34.

The ferrule components 30 thus obtained are combined into a desiredlength as discussed above, the music wire is passed through the fineholes 31 to align the connected components, roughly secure them inposition with a jig, bond them with each other, and connect the ferrulecomponents 30 to complete the ferrule 3.

The aforementioned embodiment is given to facilitate the understandingof the present invention and not intended to limit the presentinvention. Accordingly, the elements and numeric values listed in theabove embodiment allow any design change and equivalent within thetechnical scope of the present invention.

1. An optical communication ferrule for receiving an inserted opticalfiber, comprising a plurality of ferrule components having one or two ormore fine holes in which the optical fiber is inserted, the ferrulecomponents being connected with one another in an insertion direction ofthe optical fiber.
 2. The ferrule according to claim 1, wherein theplurality of ferrule components are connected such that the one or twoor more fine holes of the ferrule components to be connected arearranged in substantially a straight line.
 3. The ferrule according toclaim 1 or 2, wherein the one or two or more fine holes of the ferrulecomponents are expanded in a tapered form on at least one ends thereof.4. The ferrule according to claim 1 or 2, wherein the ferrule componenthas an adhesive filling recess or protrusion, and an injection groovefor injecting an adhesive from the outside to the adhesive fillingrecess or protrusion.
 5. The ferrule according to claim 1 or 2, whereinthe ferrule component has an engagement portion engaged with a connectorhousing in which the ferrule is set.
 6. The ferrule according to claim 1or 2, wherein the ferrule component contains zirconia ceramics.
 7. Anoptical communication ferrule for receiving an inserted optical fiber,comprising a plurality of ferrule components having one or two or morefine holes in which the optical fiber is inserted, wherein: the one ortwo or more fine holes of the ferrule components are expanded in atapered form on at least one ends thereof; and the ferrule componentsare connected to one another along an insertion direction of the opticalfiber.
 8. The ferrule according to claim 7, wherein the ferrulecomponent has an adhesive filling recess or protrusion, and an injectiongroove for injecting an adhesive from the outside to the adhesivefilling recess or protrusion.
 9. The ferrule according to claim 7 or 8,wherein the ferrule component has an engagement portion engaged with aconnector housing in which the ferrule is set.
 10. The ferrule accordingto claim 7 or 8, wherein the ferrule component contains zirconiaceramics.
 11. A manufacturing method for an optical communicationferrule that receives an inserted optical fiber, comprising: perforatingin a plurality of ferrule components one or two or more fine holes inwhich the optical fiber is inserted; and connecting the ferrulecomponents having the fine holes perforated therein such that the fineholes are arranged in substantially a straight line.
 12. Themanufacturing method for an optical communication ferrule according toclaim 11, wherein the ferrule component has a width of about 3 mm orsmaller along an arranging direction of the perforated fine holes.